The present invention is directed to bicycle derailleurs and, more particularly, to a bicycle rear derailleur having a cable guide roller for controlling the orientation of a control cable.
FIG. 1 is a side view of a prior art rear derailleur disclosed in U.S. Pat. No. 4,610,644. As shown in FIG. 1, the derailleur comprises a base member 2 for rotatably mounting to a fixing member 1 of the bicycle, a movable member 5, and two linkage members 3 and 4 that connect base member 2 and movable member 5 together so that movable member 5 is capable of movement relative to base member 2. A chain guide 6 having a guide pulley 61 and a tension pulley 62 is rotatably coupled to movable member 5 for guiding a chain 17 along a plurality of sprockets of a sprocket cluster S. A first spring 13 is disposed between the movable member 5 and the chain guide 6 for biasing chain guide 6 clockwise, and a second spring 14 is disposed between the base member 2 and the fixing member 1 for biasing base member 2 clockwise.
The derailleur is operated by a control cable C of the type having an inner wire W that slides within an outer casing O. Outer casing O is supported to base member 2 through a casing support 16, and inner wire W is connected to movable member 5 through a wire connector 15. Pulling inner wire W causes movable member 5 to move axially toward the largest sprocket S.sub.2 of sprocket cluster S, and releasing inner wire W causes movable member 5 to move axially toward the smallest sprocket S.sub.1 of sprocket cluster S. At the same time, the first and second springs 13 and 14 balance with each other to adjust the positions of the base member 2 and movable member 5 to set the radial position of the guide pulley 61 relative to the rear sprocket assembly S. As a result, base member 2 usually exhibits reciprocating motion in the direction Z.
Since control cable C is rigidly fixed to base member 2, and since control cable C ordinarily bends approximately 180.degree. before it attaches to the derailleur, control cable C resists the reciprocating motion of base member 2 during operation of the derailleur. This can adversely affect the proper positioning of the guide pulley 61. Furthermore, movement of base member 2 in the clockwise direction often causes the bend in control cable C to tighten, thus decreasing the efficiency of the cable due to increased friction between the inner wire W and the inner surface of the outer casing O.